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Thursday, July 13, 2006

Degeneracy vs Redundancy

Salvador Cordova and I have been arguing over the significance of redundancy and robustness in living systems. Salvador, has been trying to develop an "argument from redundancy" for ID creationism. It begins in an analogy between biological and engineered systems. As most ID arguments, that's where it stops as well. I'm skeptical mostly because I don't see many examples of perfect redundancy in nature.

I'm actually writing a paper on a related subject (more about that at some point) and came across an article that made the point about the difference between perfect and partial redundancy much better than I did. One of the authors is Gerald Edelman, who won the Nobel Prize for Medicine and Physiology in 1972 for his classic on the structure of antibodies. They argue that there's a difference between degeneracy in biology and redundancy in engineering:

The contrast between degeneracy and redundancy at the structural level is sharpened by comparing design and selection in engineeringand evolution, respectively. In engineering systems, logic prevails,and, for fail-safe operation, redundancy is built into design.This is not the case for biological systems. Indeed, not the leastof Darwin's achievements was to lay the argument by design torest. But, for obvious economic reasons, design is by far themajor component of most technical efforts in modern society. Ingeneral, an engineer assumes that interacting components shouldbe as simple as possible, that there are no "unnecessary" or unplannedinteractions, that there is an explicit assignment of functionor causal efficacy to each part of a working mechanism, and thaterror correction is met by feedback, modeling, or other paradigmsof control theory. Protection can be afforded by planned redundancy,but adventitious compensation for error is neither expected norusual. Irrelevancy is avoided from theoutset.

By contrast, in evolutionary systems, where there is no design, the term "irrelevant" has no a priori meaning. It is possiblefor any change in a part to contribute to overall function, mutationscan prompt compensation, stochastic interactions with the environmentcan lead to strong selection, often there is no fixed assignmentof exclusive responsibility for a given function, and, unlikethe engineering case, interactions become increasingly complex [...]